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Comment by npongratz | Hacker News Reader

In fact [Andromeda's] full diameter on the night sky is six times that of the full Moon.

I was surprised to read this. I remember gazing at Andromeda and the full moon many years ago as an amateur astronomer, but didn't have a sense of apparent size of the two.

Anyway, I dug into NASA's archives [0] which included an image showing perspective. Thought it was pretty neat, so here you go:

http://imgsrc.hubblesite.org/hu/db/images/hs-2015-02-e-compa...

[0] http://hubblesite.org/newscenter/archive/releases/2015/02/fa...

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Awesome.

I was lucky enough to see Andromeda with the naked eye while doing a transatlantic yacht race. Believe it or not it took me a couple of days to find Pegasus but then it was obvious each night as I gazed up at the sky.

We're on a collision course with Andromeda, right? Those trillion stars crashing in are going to make for a wonderful fireworks display :)

You are right about the collision course. The two will slowly merge into a bigger galaxy like in this picture: http://cas.sdss.org/dr6/en/proj/basic/galaxies/images/752-6-...

Wikipedia also has a video but this picture also illustrates it well: https://en.wikipedia.org/wiki/Andromeda%E2%80%93Milky_Way_co...

The thing is, stars are so far apart from each other that there won't be any collisions. From wikipedia: "While the Andromeda Galaxy contains about 1 trillion (1012) stars and the Milky Way contains about 300 billion (3×1011), the chance of even two stars colliding is negligible because of the huge distances between the stars."

link: http://en.wikipedia.org/wiki/Andromeda–Milky_Way_collision

You're correct, the likelihood of stars colliding is near zero, but the gas that forms stars in both galaxies will collide and that will create quite a spectacular view. It will likely resemble something like this: http://hugepic.io/bfc195a2b/4.00/2.02/-77.61

Space is full of a LOT of empty space. Maybe even more amazing to myself, is the scale works almost the same in inverse. There's also a lot of space at the tiniest scales.

Scale of our solar system: http://joshworth.com/dev/pixelspace/pixelspace_solarsystem.h...

We represented both galaxies in 3D crystal cubes in case that's of interest: http://cosmic3d.com/

Nice. I've been looking for that; only found some Japanese outfit that made one years ago, for (the yen equivelent of) $100 ... out of my price range. Glad to see yours is much more reasonable.

Curious about accuracy ... how many bubbles (stars) are etched?

There is a neat size comparison of the Andromeda galaxy (178 x 63 arc minutes) and the moon (30 x 30 arc minutes) on APOD: http://apod.nasa.gov/apod/ap061228.html

According to wikipedia "Although it appears more than six times as wide as the full Moon when photographed through a larger telescope, only the brighter central region is visible to the naked eye or when viewed using binoculars or a small telescope." [1]

[1] http://en.wikipedia.org/wiki/Andromeda_Galaxy

Yes, exposure time (and aperture size) makes all the difference. Most of the disk is quite dim.

Another stunning thing about Andromeda to observe is its satellite galaxies. The larger satellite galaxies are easily observable in a wide-field eye-piece even by beginners. The smaller ones (globular clusters) are a little harder.

Observing the large central galaxy alongwith its satellite galaxies gives me a better sense of scale and fills me with awe.

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